The present invention relates to a system of plugs, distributors and switches for light guides, in which the light guides are coupled with each other by image-forming optical elements.
For the detachable connection of two optical fibers use is predominantly made of plugs by which the optical fibers mounted therein come into direct contact after their end surfaces have been placed together. Due to the high requirements on the accuracy of the centering of such plugs, necessary in particular in the case of monomode fibers, they are expensive to manufacture. In the case of adjustable embodiments they must upon replugging in each case be precisely adapted to the new mating plug.
A similar picture is present in the case of light-guide switches or distributors. They consist of light guides firmly connected to each other which are arranged at their ends against each other or on a coupling plate, or else of fibers which are fused together. In such distributors the coupling ratio of the individual fibers is substantially fixed. It can still be influenced only under extremely high requirements as to precision with reference to the mechanism used, as described, for instance, in U.S. Pat. No. 3,874,779 or, when using polarized light, by applying external electromagnetic fields to the distributor, as described in DE-OS No. 28 53 149.
From West German Petty Patent No. 74 30 490, West German Unexamined Application for Patent No. 19 41 923 and U.S. Pat. No. 4,119,362 light-guide couplings are known in which one or more optical imaging-forming elements are used. The solutions described therein are, however, not adapted to reduce the demands on the precision of the centering of the light guides to be coupled.
It has also already been proposed to provide each of the light-guide plugs to be connected with a biconvex lens at the focal point of which the end surface of the corresponding light guide is arranged. Problems as to the centering of the two plugs with respect to each other are substantially avoided by the coupling in the widened parallel ray path of the plug connection. Since spherical lenses, in connection with the short focal lengths required for small plug dimensions, can, however, be adapted only poorly to the radiation characteristic of a glass fiber and because of the many glass-air interfaces such plugs, however, have relatively high coupling losses.
The object of the present invention is to create a device for connecting light guides which, with only slight coupling losses and without any great demand as to the dimensional precision of the movable or detachable parts, makes it possible to manufacture at low cost the inter-compatible components of a connector system such as plugs, distributors and switches.
This object is achieved in accordance with the body of the claims.
In both solutions for a device for the connecting of light guides the number of interfaces between media of different indices of refraction is minimized since the beam-widened optical elements are in direct contact with each other for instance by means of immersion oil or are placed directly on the light guides. The necessary refractive power is provided only by one, for instance aspherical, glass-air interface.
In addition, the advantages of the lens-plug principle, namely lack of sensitivity of the interfaces in the widened beam path to misadjustments of the parts coupled to each other are retained. Spacing errors between bushing and plug are of no importance in the case of a parallel ray path and lateral offset affects the coupling losses merely by an amount reduced by the ratio of light-guide diameter to lens diameter.
It need merely be seen to it that the bearing surfaces of plug and bushing extend parallel to the optical axes of the optical elements contained therein. This requirement can easily be satisfied upon the manufacture of the plugs. Subsequent centering of the plugs with respect to each other by the user is unnecessary.
For the solution indicated, aspherical refractive surfaces are selected in order to minimize the aperture errors of the two lenses forming a biconvex element which rest against each other in the immersion contact and thus to assure a sufficiently punctiform imaging of the light-guide end surfaces with an aperture which is adapted to their radiation characteristic.
In the solution shown in FIG. 2 with biconvex refractive surfaces and the medium, glass, between the light guide end surfaces and the vertex of the "air lens," the aperture defect remains within tolerable orders of magnitude even when spherical surfaces are used.
The device in accordance with the invention can be applied not only to plugs which serve for instance to connect two light guides together but it also includes distributors (light-guide branching) as well as switches and valves in which the coupling ratio of the connected light guides can be varied in discrete steps or continuously. They consists of a suitable housing provided with at least three bushings to receive the above-described plug connections, within which housing beam splitters or mirrors are arranged fixed or movable.
As beam splitters there are suitable, for instance, partially mirrored prisms or flat plates which distribute the incident light, independent of wavelength over a corresponding number of outputs. If the beam splitters are developed in the manner of interference filters, there is obtained an optical demultiplexer which distributes a multispectral light signal in wavelength-selective manner over the individual outputs.
In the same way as in the case of the detachable plug connections, a reduction in the requirements as to tolerance of the moved part are obtained also for switches and valves if said part is located in the widened ray path. The larger tolerances permitted by the lens-plug principle for the first time make it possible to create valves and switches for light-guide cables with which problemless continuous operation is possible.
In the case of switches or distributors the connections of which are frequently opened the imaging optical elemtns are preferably, as described above, integrated in the plugs themsleves. If such light regulators are intended, however, for fixed light-guide cabling then it is advantageous to arrange the imaging optical elements in the switch and to connect the light guide securely to the regulator or switch, for instance via a conventional centering plug. The lenses can then be produced in one piece by injection molding and in one particularly advantageous embodiment directly as part of the housing which contains the movable beam splitter.